Very Large Scale Integrated (VLSI) circuit devices have become so dense that, for example, semiconductor circuits smaller than 1.0 micrometers are now being employed. One of the drawbacks of increasing the density of an integrated circuit device is the difficulty of maintaining electrical isolation of one circuit from another. When one circuit inadvertently couples electrically with another circuit, the device will malfunction and a fault will be recorded. This type of failure occurs in normal operation and to a greater degree when radiation is also present, such as in communication satellites. The other drawback of increasing the density of an integrated circuit is insufficient dissipation of heat generated by the chip, resulting in a rise of junction temperature. This rise in junction temperature reduces efficiency and reliability, and sometimes causes the chip to short circuit.
In an effort to improve electrical isolation between circuits and heat dissipation efficiency of the chip, the electronics industry has been experimenting with multi-layer composite structures coated with one or more layers of PCD. These PCD films have been successfully deposited using a number of chemical vapor deposition (CVD) techniques including hot filament CVD (HFCVD), RF plasma-assisted CVD, microwave plasma-assisted CVD, DC plasma assisted CVD, DC plasma jet, and laser-assisted CVD. The electrical properties such as resistivity and breakdown voltage of PCD layers deposited by the above techniques have generally been low and therefore unacceptable to the electronics industry.
A number of technical papers and patents have been published which describe the deposition and properties of PCD produced by various techniques. For example, technical papers by B. V. Spitsyn, et al., entitled, "Vapor Growth of Diamond on Diamond and Other Surfaces", published in Journal of Crystal Growth, Vol. 52, pp. 219-226 (1981), D. V. Fedoseev, et al., entitled "Synthesis of Diamond in Its Thermodynamic Metastability Region", published in Russian Chemical Reviews, Vol. 53(5), pp. 435-444 (1984), and B. V. Derjaguin and D. B. Fedoseev entitled "The Synthesis of Diamond at Low Pressure", Scientific American, Vol. 233(5), pp. 102-9 (1975), discussed diamond deposition on a number of substrates. These papers neither disclose nor suggest a process of depositing diamond film with enhanced, that is, at least partially ordered crystal orientation and consequently the authors of these papers had no concept of the advantages of such a process.
M. W. Geis has described deposition of (111) textured diamond films on smooth substrates using diamond seeds in a paper entitled "Growth of Textured Diamond Films on Foreign Substrates from Attached Seed Crystals," published in Appl. Phys. Lett., Vol. 55(6), pp. 550-552 (1989). This paper does not describe a process for depositing diamond with enhanced crystal orientation in the (220) or (311) and (400) directions relative to the (111) directions, or with high electrical resistivity.
U.S. Pat. No. 4,434,188, issued 28 Feb. 1984 and a paper by K. Ito, et al. entitled, "Diamond Synthesis by the Microwave Plasma CVD Method Using a Mixture of Carbon Monoxide and Hydrogen Gas (I)", published in Chemistry Letters, pp. 589-592 (1988) describe the deposition of diamond films by microwave plasma CVD technique using mixtures of either hydrogen and hydrocarbon or hydrogen and carbon monoxide. These references do not disclose the deposition of diamond films with enhanced crystal orientation and high resistivity.
A technical paper by B. Singh, et al. entitled, "Hollow Cathode Plasma Assisted Chemical Vapor Deposition of Diamond", published in Appl. Phys. Lett., Vol. 52(20), pp. 1658-1660 (1988) describes the deposition of diamond films by hot cathode plasma CVD using a mixture of hydrogen and hydrocarbon. European Patent Publication No. 0320657, published 21 Jun. 1989, discloses deposition of diamond films using a combination of hot filament and microwave CVD techniques. These references do not disclose a process for depositing diamond films with enhanced crystal orientation or with high electrical resistivity.
A. Sawabe, et al., describe deposition of diamond films by DC plasma CVD using a mixture of hydrogen and methane in a paper entitled, "Growth of Diamond Thin Films in a DC Discharge Plasma", published in Applied Surface Science, Vol. 33/34, pp. 539-545 (1988). This paper does not disclose a process for depositing diamond films with enhanced crystals orientation or with high electrical resistivity.
Japanese Kokai Patent No. Sho 64(1989)-65092, published 10 Mar. 1989, and Japanese Kokai Patent No. Sho 62(1987)-202897, published 7 Sep. 1987, describe processes for depositing thin and adherent diamond films on substrates using a metal or metal carbide interlayer deposited on the substrates by PVD. Japanese Kokai Patent No. Sho 64(1989)-61397, published 8 Mar. 1988, describes a process of depositing thin diamond films adherently on cutting tools by first embedding fine diamond particles on tool substrates. These patent applications neither describe a process for depositing diamond films with enhanced crystal orientation nor discuss the advantages of these films.
A number of technical papers by S. Matsumoto, et al. entitled, "Growth of Diamond Particles from Methane-Hydrogen Gas", published in J. Materials Service, Vol. 17, pp. 3106-3112 (1982), "Chemical Vapor Deposition of Diamond From Methane-Hydrogen Gas", published in Proc. 7th ICVM, Tokyo, Japan, pp. 386-391 (1982), and "Vapor Deposition of Diamond Particles from Methane," published in Japanese Journal of Applied Physics, Vol. 21, No. 4, pp. L183-L185 (1982), describe deposition of diamond films by a hot filament CVD technique. Technical papers by B. Singh, et al. entitled, "Growth of Polycrystalline Diamond Particles and Films by Hot-Filament Chemical Vapor Deposition", submitted for publication in J. Vac. Sci. Tech. (1988) and "Effects of Filament and Reactor Wall Materials in Low-Pressure Chemical Vapor Synthesis of Diamond", published in Appl. Phys. Lett., Vol. 52(6), pp. 451-452 (February, 1988) also describe deposition of diamond films by the hot filament CVD technique. None of the foregoing papers disclose a process for depositing diamond films with either enhanced crystal orientation or high electrical resistivity.
P. O. Joffreau, et al. disclose a hot filament CVD process for depositing diamond films on refractory metals in a paper entitled, "Low-Pressure Diamond Growth on Refractory Metals", published in R&HM, pp. 186-194 (December 1988). Another paper by T. D. Moustakas, entitled, "The Role of the Tungsten Filament in the Growth of Polycrystalline Diamond Films by Filament Assisted CVD of Hydrocarbons", published in Solid State Ionics, Vol, 32/33, pp. 861-868 (1989) describes an HFCVD process for depositing diamond films. These papers, once again, do not disclose a process for depositing diamond films with either enhanced crystal orientation or high electrical resistivity.
A technical paper by E. N. Farabaugh, et al. entitled, "Growth of Diamond Films by Hot Filament Chemical Vapor Deposition", published in SPIE, Vol. 969 Diamond Optics, pp. 24-31 (1988), discloses a process for depositing diamond films by HFCVD. These diamond films were deposited using a wide range of temperature, analyzed by x-ray diffraction and shown to have no preferred crystal orientation. Therefore, this paper does not disclose a process for depositing diamond films with either enhanced crystal orientation or high electrical resistivity.
U.S. Pat. Nos. 4,707,384 and 4,734,339 disclose an HFCVD process for depositing one or more polycrystalline diamond layers on a variety of substrates. These patents do not disclose a process for depositing diamond films with enhanced crystal orientation or with high electrical resistivity.
Japanese Kokai Patent No. Sho 62(1987)-119, published 6 Jan. 1987, discloses a HFCVD process for depositing diamond films on substrates with a variety of interlayers. Japanese Kokai Patent No. Sho 62(1987)-171993, published 28 Jul. 1987, discloses a CVD process for depositing diamond films using a mixture of an organic compound and a reaction gas containing at least one species of boron, aluminum, gallium, indium, thallium, nitrogen, phosphorus, arsenic, antimony or bismuth. Japanese Kokai Patent No. Sho 63(1988)-297299, published 5 Dec. 1988, discloses a process for depositing diamond films using a mixture of hydrogen, hydrocarbon, chlorine and inert gas. Japanese Kokai Patent No. Sho 63(1988)-153815, published 27 Jun. 1988, discloses a HFCVD process for depositing diamond films using tungsten filament. None of the foregoing patent applications disclose processes for depositing diamond films with either enhanced crystal orientation or high electrical resistivity.
Japanese Kokai Patent No. Sho 63(1988)-166797, published 9 Jul. 1988, discloses the use of filaments made of an alloy of Ta, Zr and/or Hf for enhancing filament life during HFCVD process. This application does not disclose the deposition of diamond films with enhanced crystal orientation or with high electrical resistivity.
Japanese Kokai Patent No. Sho 63(1988)-159292, published 2 Jul. 1988, discloses a DC current biased HFCVD process for depositing diamond films on a substrate with a large surface area or with a curved surface. It does not disclose the formation of diamond films with enhanced crystal orientation or with high electrical resistivity.
R. G. Buckley, et al. disclose an HFCVD process for depositing diamond films in a paper entitled, "Characterization of Filament-Assisted Chemical Vapor Depositing Diamond Films Using Raman Spectroscopy", published in J. Appl. Phys., 66 (8), 3595-3599 (1989). T. Kawato and K. Kondo disclose the effect of adding oxygen along with feed gas mixture upon diamond films deposited by HFCVD in a paper entitled, "Effect of Oxygen on CVD Diamond Synthesis", published in Japanese Journal of Applied Physics, Part I, Vol. 2 (9), pp. 1429-1432 (1987). These papers do not disclose a method for depositing diamond films with either enhanced crystal orientation or high electrical resistivity.
U.S. Pat. No. 4,816,286 and a paper by Y. Hirose and Y. Terasawa entitled, "Synthesis of Diamond Thin Films by Thermal CVD Using Organic Compounds", published in Japanese Journal of Applied Physics, Vol. 25(6), pp. L519-L521 (1986) disclose a CVD method for depositing diamond films using a mixture of hydrogen and an organic compound containing carbon, hydrogen, and at least one of oxygen and nitrogen. Japanese Kokai Patent No. Sho 64(1989)-24093, published 26 Jan. 1989, discloses a CVD method of depositing diamond films using a mixture of an organic compound and water vapors. Japanese Kokai Patent No. Sho 63(1988)-307195, published 14 Dec. 1988, discloses a CVD method of depositing diamond films using a mixture of an organic compound and a raw gas containing ammonia. These references do not describe a method of depositing diamond films with either enhanced crystal orientation or with high electrical resistivity.
U.S. Pat. No. 4,859,490 and European Patent Publication Nos. 0 254 312 and 0 254 560 disclose HFCVD processes for depositing diamond films. These references teach that diamond films with high electrical resistivity can not be produced by HFCVD, and that high resistivity diamond films can only be produced by using a combination of hot-filament and plasma generated by either microwave or DC discharge during chemical vapor deposition. These patents teach away from using an HFCVD process to produce diamond films having enhanced crystal orientation and high electrical resistivity.
U.S. Pat. No. 4,783,368 makes reference in column 2, lines 22-32, to the very poor electrical insulating properties, particularly dielectric breakdown, that are obtained when thin layers of polycrystalline diamond are deposited by CVD techniques. This reference goes on to describe and claim a method of producing an insulating layer comprising a diamond or diamond-like carbon material and an element from group IVA on a substrate by applying DC voltage and RF power to the substrate and a magnetic field parallel to the substrate's surface. Examples are given in which the transmission electron diffraction of the diamond-like carbon layers corresponded to (111) and (220) of natural diamond. This patent does not disclose a process for depositing diamond films with enhanced crystal orientation.
Japanese Kokai patent No. Sho 63(1988)-307196, published 14 Dec. 1988, discloses a plasma CVD process for depositing multilayered diamond films. The first layer deposited on the substrate is made of microcrystal diamond and the second layer deposited on the top of the first layer is formed with crystalline facet with (110) or (220) orientation. The application discloses that if the methane concentration in the feed gas is smaller than about 1%, the deposited films have randomly oriented crystals. However, if the concentration of methane is higher than 1%, the films show enhanced crystal orientation in the (220) direction. The deposited films are disclosed to have good thermal conductivity. This patent does not disclose a process for depositing diamond films either with enhanced crystal orientation in both the (220) or (311) direction and the (400) direction, or with high electrical resistivity.
K. Kobashi, et al., disclose a microwave plasma CVD process for depositing diamond films with enhanced crystals orientation in (100) or (400) direction in papers entitled, "Synthesis of Diamonds by Use of Microwave Plasma Chemical Vapor Deposition: Morphology and Growth of Diamond Films", published in Physical Review Bulletin of the American Physical Society, Vol. 38(6), pp. 4067-4084 (1988) and entitled "Summary Abstract: Morphology and Growth of Diamond Films", published in J. Vac. Sci. Techn. Vol. A6(3), pp. 1816-1817 (1980). These papers disclose depositing films with (111) crystal orientation at methane concentration &lt;0.4% and films containing diamond crystals oriented in (100) direction at methane concentration above 0.4%. The films deposited at methane concentration .about.1.6% have been shown to be structureless. W. Zhu, et al., disclose a microwave plasma CVD process for depositing diamond films with enhanced crystals orientation in either (111) or (100) directions in a paper entitled, "Effects of Process Parameters on CVD Diamond Films", published in J. Mater. Res., Vol. 4(3), pp. 659-663 (1989). This paper discloses the disposition of diamond films with enhanced crystals orientation in (110) direction with less than 2% methane in hydrogen at temperatures between 910.degree.-950.degree. C. A higher temperature (&gt;1000.degree. C.) is claimed to favor the formation of crystals oriented in the (111) direction. An intermediate temperature (950.degree.-1000.degree. C.) has been shown to favor formation of crystals oriented in (111) and (100) directions with neither predominating. N. Setaka discloses a CVD method of depositing diamond films in a paper entitled, "Diamond Synthesis From Vapor Phase and its Growth Process", published in J. Mater. Res., Vol. 4, No. 3, pp. 664-670 (1989). The paper discloses that films deposited with 0.5% methane contained crystal oriented in (111) and (100) directions. It also discloses that as the methane concentration approaches 3%, a remarkable enhancement of crystal orientation in (220) direction relative to (111) is observed. Despite the fact that the authors of these papers have recognized enhanced crystal orientation in one plane relative to (111) plane, none of them disclose the formation of diamond films with enhanced crystal orientation in at least two planes relative to (111) plane nor a process for achieving diamond films having such crystal orientation as well as high electrical resistivity.
Although the polycrystalline diamond films deposited by the techniques described in the foregoing references have been shown to have good thermal conductivity, i.e., of not less than 50 W/mk, their use in the electronic industry has been limited due to poor electrical properties. Several attempts have been made by numerous researchers to produce polycrystalline diamond films with good electrical properties, but with limited success. For example, in two recent papers by K. V. Ravi and M. I. Landstrass one entitled "Silicon on Insulator Technology using CVD Diamond Films", published in PMAC, Electrochem Soc., 24-37 (1989) and the other entitled, "Resistivity of Chemical Vapor Deposited Diamond Films", published in Appl. Phys. Letter, Vol. 55(10), pp. 975-977(1989), it is disclosed that the poor electrical properties of DC plasma and microwave plasma deposited polycrystalline diamond films are due to the presence of dissolved hydrogen. The authors disclose that the dissolved hydrogen can be removed from the films by annealing, thereby improving the electrical properties. The authors neither present the electrical properties of hot-filament deposited polycrystalline diamond films nor describe the effect of annealing on the electrical properties of HFCVD films. Furthermore, the authors do not disclose the formation of diamond films with enhanced crystal orientation.
Contrary to the teaching of K. V. Ravi and M. I. Landstrass, the diamond films deposited by HFCVD contain only trace amounts of hydrogen (compared to films deposited by DC plasma or microwave plasma CVD) to begin with and the annealing process only results in marginal improvements in their electrical properties. However, it has been found in the present invention that the electrical properties (i.e. electrical resistance and breakdown voltage) of polycrystalline diamond films can be significantly improved over such polycrystalline diamond systems of the prior art by depositing diamond crystals with enhanced orientation.
Further, the polycrystalline diamond films deposited by the prior art techniques have a poor surface finish due to the presence of randomly oriented faceted crystals. Thus, the surface finish of polycrystalline diamond films can also be significantly enhanced by depositing diamond crystals with enhanced orientation on at least two planes.